Page:NIOSH Manual of Analytical Methods - 2516.pdf/3

 DICHLOROFLUOROMETHANE: METHOD 2516, Issue 2, dated 15 August 1994 - Page 3 of 4 b.

9.

10.

Immediately before adding dichlorofluoromethane, withdraw from each vial an amount of air equal to that of dichlorofluoromethane to be added. c. Slowly bubble a measured amount of dichlorofluoromethane into the liquid in each vial using a gas-tight syringe. d. Analyze together with samples and blanks (steps 11 and 12). e. Prepare calibration graph (ratio of peak area of analyte to peak area of internal standard vs. mg dichlorofluoromethane). Determine desorption efficiency (DE) at least once for each lot of charcoal used for sampling in the calibration range (step 8). Prepare three tubes at each of five levels plus three media blanks. a. Inject a known amount of dichlorofluoromethane slowly and directly into a medial blank front sorbent section with a gas-tight syringe. b. Cap the tube. Allow to stand overnight. c. Desorb (steps 5 through 7) and analyze together with working standards (steps 11 and 12). d. Prepare a graph of DE vs. mg dichlorofluoromethane recovered. Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration graph and DE graph are in control

MEASUREMENT: 11.

12.

Set gas chromatograph according to manufacturer's recommendations and to conditions given on page 2516-1. Inject sample aliquot manually using solvent flush technique or with autosampler. t r = 6 min under these conditions. NOTE 1: If an autosampler is used, transfer an aliquot of the sample solution to a sealed empty vial using a syringe needle as a vent. NOTE 2: If peak area is above the linear range of the working standards, dilute with eluent, reanalyze, and apply the appropriate dilution factor in calculations. Measure peak area. Divide the peak area of analyte by the peak area of internal standard of the same chromatogram.

CALCULATIONS: 13.

14.

Determine the mass, mg (corrected for DE) of dichlorofluoromethane found in the sample front (W f) and back (W b) sorbent tubes, and in the average media blank front (B f) and back (B b) sorbent tubes. NOTE: If W b > W f/10, report breakthrough and possible sample loss. Calculate concentration, C, of dichlorofluoromethane in the air volume sampled, V (L):

EVALUATION OF METHOD: Method S109 was issued on September 30, 1976 [2], and validated over the range 2100 to 12,600 mg/m 3 by analyzing 18 spiked samples and 18 samples collected from dynamically-generated atmospheres of dichlorofluoromethane gas [1,4]. These recoveries were 100.9 and 102.9%, respectively. A combined storage migration study determined that samples of 17 and 35 mg had a 100% recovery after seven days if stored without backup sections. At the same levels, those front sections stored with backup sections had 83.2% recovery. Breakthrough (5%) in an atmosphere of 9120 mg/m 3 and 90% RH, sampling at 0.187 L/min, occurred at 23 min. giving a breakthrough volume of 4.3 L and tube capacity of 39 mg. In a dry atmosphere of 8850 mg/m 3, breakthrough occurred after 64 min sampling at 0.187 L/min, giving a breakthrough volume of 12.0 L and tube capacity of 102 mg. Desorption efficiencies averaged 101% over the range 5.9 to 34 mg dichlorofluoromethane per sample.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94